Water cortisol and testosterone in Nile tilapia (Oreochromis niloticus) recirculating aquaculture systems

RAS containing Nile tilapia, cortisol and testosterone are released to the culture water. Water cortisol concentration depends on the water exchange rate that is used and higher concentrations are expected in lower water exchange rates. Fish grading and weighing has a short-term effect on the water cortisol concentrations, after which concentrations return to the basal levels. These findings show that reduction in water usage and fish handling may lead to a significant increase of hormones in the rearing water, which emphasizes the importance of accounting for steroids in the design and management of RAS.